1. Field of the Invention
The present invention relates to an ultrasonic probe for probing into hollow objects such as hollow organs of a living body and other hollow constructions. More particularly, the invention relates to an ultrasonic probe having a piezoelectric transducer to be inserted in hollow organs such as the blood vessels of a living body.
2. Description of the Prior Art
There has been a widespread use of ultrasonic diagnostic systems having an ultrasonic probe inserted in blood vessels and other hollow organs of a living body for diagnostic purposes. Hereinafter, the ultrasonic probe inserted in blood vessels is explained. The operating principle of the ultrasonic probe is the same whether it is used in a hollow organs of the human body or in other hollow objects under examination. FIG. 35 is a schematic view showing how an ultrasonic probe is inserted illustratively in blood vessels of a living body. In FIG. 35, the rear end of an ultrasonic probe 12 is connected to an ultrasonic diagnostic system 10. The front end of the probe 12 is inserted from the thigh of a patient 1 into blood vessels before reaching the patient's affected part. The front end of the ultrasonic probe 12 has a piezoelectric transducer that transmits ultrasonic waves and receives their reflection from the affected part. The received signal of the probe 12 is sent to the ultrasonic diagnostic system 10. A monitor screen 11 attached to the system 10 displays an image based on the signal for diagnostic purposes.
FIG. 36 is a schematic view outlining the structure of a typical prior art ultrasonic probe, highlighting the front end thereof (the probe's front end will also be generically called the "ultrasonic probe" hereafter). In FIG. 36, the ultrasonic probe 12 is covered with a tube 13 and tipped with a piezoelectric transducer 14. The piezoelectric transducer 14 is connected to the diagnostic system 10 through lead wires. Opposite to the piezoelectric transducer 14 is a reflector 18 having an oblique reflecting surface 18a.
When a signal is sent from the diagnostic system 10 over the lead wires 16 to the piezoelectric transducer 14, the transducer 14 generates ultrasonic waves 15 toward the reflector 18. The ultrasonic waves are reflected by the reflecting surface 18a of the reflector 18 for transmission into the living body. Tissues in the living body reflect the ultrasonic waves and send them back to the ultrasonic probe 12. The reflected ultrasonic waves are again reflected by the reflecting surface 18a and received by the piezoelectric transducer 14. The received signal of the probe 12 is transmitted to the diagnostic system 10 through the lead wires 16.
One end of a flexible shaft 20 is coupled to the reflector 18. The other end of the flexible shaft 20 is connected to the shaft of a motor 25 incorporated in the diagnostic system 10. As the motor 25 rotates, the torque is transmitted to the reflector 18 via the flexible shaft 20, thus rotating the reflector 18. This allows the ultrasonic waves from the piezoelectric transducer 12 to probe the blood vessel circumferentially, producing a sectional view of the blood vessel under examination.
In the rear of the reflector 18 is a partition plate 22 that seals the front end of the probe from the rest. The sealed space is filled with acoustic coupling substance, for example physiological salt water, of which the acoustic impedance is approximately the same as that of the living body.
FIG. 37 is a schematic view of another prior art ultrasonic probe. In this figure and other figures that follow, those component parts having the same functions as their counterparts in FIG. 36 are designated by like reference numerals regardless of their differences in specific constructions. Descriptions of these parts will be omitted if they are repetitive, and only the significant differences therebetween will be described. In the example of FIG. 37, a motor 32 for rotating the reflector 18 is built in an ultrasonic probe 30. The motor 32 is connected to the diagnostic system 10 through the lead wires 34.
FIGS. 38 and 39 are schematic views of other prior art ultrasonic probes. The ultrasonic probe 40 of FIG. 38 has the piezoelectric transducer 14 fixed crosswise with respect to a flexible shaft 42. Moving the flexible shaft 42 lengthwise causes ultrasonic waves 15 to scan linearly the object under examination. The ultrasonic probe 50 of FIG. 39 is also used for linear scanning. In this construction, the piezoelectric transducer 14 is fixed to a rotor 52 of a linear motor. The stator 54 of the linear motor is secured to the inner wall of the tube 13.
Of these prior art ultrasonic probes outlined above, those in FIGS. 36 and 38 using the flexible shaft or the like to rotate or move the reflector or piezoelectric transducer have a major disadvantage. That is, the relative rigidity of the flexible shaft or its equivalent detracts from the flexibility of the ultrasonic probe as a whole. This makes it difficult for the probe operator to insert the ultrasonic probe illustratively into bent blood vessels in order to reach the affected part of the living body.
The prior art ultrasonic probes shown in FIGS. 37 and 39 contain a motor inside and thus do away with the flexible shaft. Removing the flexible shaft or its equivalent ensures good flexibility and operability of the ultrasonic probe. However, with the motor incorporated inside, ultrasonic probes of this kind necessarily have greater outer diameters. The enlarged outer diameter makes it impossible to insert the probe in fine blood vessels and similar hollow objects.